1. Field of the Invention
The present invention relates to a panel assembly made up of an outer member and an inner member, which overlap each other and jointly have an edge that includes a distal end portion of the outer member and a distal end portion projecting from an end of the inner member, the distal end portions being fastened together by sheet metal seaming. The present invention also relates to a method of forming such a panel assembly.
2. Description of the Related Art
Heretofore, in the automobile industry, panel assemblies, which are made up of an outer panel (outer member) and an inner panel (inner member) that overlap each other and have respective edges fastened together, have widely been used as engine hoods, trunk lids, doors, etc.
Certain panel assemblies of the type described above may be of a three-dimensional shape having different curvatures on the edges thereof, or may be made up of panels having portions of different rigidities, shapes, and other qualities. A panel assembly has been proposed having edges of excellent appearance, and which is made up of members fastened together with high strength (see Japanese Laid-Open Patent Publication No. 2008-105083).
The proposed panel assembly has a seamed edge having a first shape and a second shape. The first shape is a seamed shape in which an end of a first panel member is included in a second panel member, and an end of the second panel member is included in the first panel member. The second shape is a seamed shape in which an end of the second panel member is included in the first panel member, but an end of the first panel member is not included in the second panel member.
As shown in FIG. 10 of the accompanying drawings, one panel assembly is made up of an outer panel 1 and an inner panel 2. The outer panel 1 and the inner panel 2 are fastened together by sheet metal seaming. The inner panel 2 has a distal end portion 2b that projects from an end 2a thereof toward a distal end portion 1a of the outer panel 1.
The inner panel 2 overlaps and is spaced inwardly from the outer panel 1. In order to fasten the outer panel 1 and the inner panel 2, the distal end portion 1a of the outer panel 1 is curled initially in the forming direction D toward the inner panel 2. As the distal end portion 1a is curled, the distal end portion 1a encloses the distal end portion 2b of the inner panel 2 and is continuously curled up to an end line 3.
The distal end portion 2b of the inner panel 2 has a forming width W that increases at boundary regions 4 between the distal end portion 2b and the end 2a. Therefore, when a curling punch is used to curl the distal end portions 1a, 2b, the curling punch is subjected to excessive resistance (resistive load per unit width×forming width) at the boundary regions 4. As a result, the resultant seamed edge is likely to have a poor appearance due to scratches, dents, and other damage caused by improper biting engagement with the curling punch.